A prior-art circuit breaker will be described below.
FIGS. 1 to 3 are sectional views showing a conventional circuit breaker, wherein FIGS. 1 to 3 show different operating states.
Numeral 1 designates a cover, and numeral 2 a base, which forms an insulating container 3 with the cover 2. Numeral 4 designates a stationary contactor, which has a stationary conductor 5 and a stationary contact 6 at one end of the conductor 5, and the other end of the conductor (not shown). Numeral 7 designates a movable contact 9 disposed oppositely to the contact 6 at one end of the conductor 8. Numeral 10 designates a movable contactor unit, and numeral 11 a movable element arm, which is attached to a crossbar 12 so that each pole is constructed to simultaneously open or close. Numeral 13 designates an arc extinguishing chamber in which an arc extinguishing plate 14 is retained by a side plate 15. Numeral 16 designates a toggle linkage, which has an upper link 17 and a lower link 18. The link 17 is connected at one end thereof to a cradle 19 through a shaft 20 and at the other end thereof to one end of the link 18 through a shaft 21. The other end of the link 18 is connected to the arm 11 of the contactor unit 10. Numeral 22 designates a tiltable operation handle, and numeral 23 an operation spring, which is provided between the shaft 21 of the linkage 16 and the handle 22. Numerals 24 and 25 respectively designate a thermal tripping mechanism and an electromagnetic gripping mechanism, which are respectively defined to rotate a trip bar 28 counterclockwise via a bimetallic element 26 and a movable core 27. Numeral 29 designates a latch, which is engaged at one end thereof with the bar 28 and at the other end thereof with the cradle 19.
When the handle 22 is tilted down to the closed position in the state that the cradle 19 is engaged with the latch 29, the linkage 16 extends, so that the shaft 21 is engaged with the cradle 19, which the result that the contact 9 is brought into contact with the contact 6. This state is shown in FIG. 1. When the handle 22 is then tilted down to the open position, the linkage 16 is bent to isolate the contact 9 from the contact 6, and the arm 22 is engaged with a cradle shaft 30. This state is shown in FIG. 2. When an overcurrent flows in the circuit when the circuit breaker is in the closed state shown in FIG. 1, the mechanism 24 or 25 operates, the engagement of the cradle 19 with the latch 29 is disengaged, the cradle 19 rotates clockwise around the shaft 30 as a center, and is abutted against stop shaft 31. Since the connecting point of the cradle 19 and the link 17 exceeds the operating line of the spring 23, the linkage 16 is bent by the elastic force of the spring 23, each pole automatically cooperatively breaks the circuit via the bar 12. This state is shown in FIG. 3.
The behavior of an arc which is generated when the circuit breaker breaks the current will be described below.
When the contact 9 is contacted with the contact 6, the electric power is supplied sequentially from a power supply side through the conductor 5, the contacts 6 and 9 and the conductor 8 to a load side. When a large current such as a shortcircuiting current flows in this circuit in this state, the contact 9 is isolated from the contact 6 as described before. In this state, an arc 32 is generated between the contacts 6 and 9, and an arc voltage is produced between the contacts 6 and 9. Since this arc voltage rises as the distance from the contact 6 to the contact 9 increases the arc 32 is tripped by the magnetic force toward the plate 14 to be extended, and the arc voltage is further raised. In this manner, the arc current approaches the current zero point, thereby extinguishing the arc to complete the breakage of the arc. The huge injected arc energy eventually becomes thermal energy, and is thus dissipated completely out of the container, but transiently rises the gas temperature in the small container and accordingly causes an abrupt increase in the gas pressure. This causes a deterioration in the insulation in the circuit breaker and an increase in the quantity of discharging spark escaping from the breaker, and it is thereby feared that an accident of a power source shortcircuit or damage to the circuit breaker body will occur.
The mechanism of the arc energy consumption based on the creation of the present invention will be described below.
FIG. 4 is a view in which an arc A is produced between contactors 4 and 7. In FIG. 4, character T designates a flow of thermal energy which is dissipated from the arc A through the contactors, character the flows of the energy of metallic particles which are released from the arc space, and character R the flows of energy caused by light which is irradiated from the arc space. In FIG. 4, the energy injected into the arc A is generally consumed by the flows T, m and R of the above three energies. The thermal energy T which is conducted to electrodes of these energies is extremely small, and most of the energies are carried away by the flows m and T. In the mechanism of the consumption of the energy of the arc A, it has heretofore been considered that the flows m in FIG. 4 are almost all of these energizes, and the energy of the flows R is substantially ignored, but it has been clarified by the recent studies of the present inventors that the consumption of the energy of the flows R and hence the energy of light is so huge as to reach approx. 70% of the energy injected to the arc A.
In other words, the consumption of the energy injected to the arc A can be analyzed as below. EQU P.sub.W =V.multidot.I=P.sub.K +Pth+P.sub.R EQU P.sub.K =1/2mV.sup.2 +m.multidot.C.sub.p .multidot.T
where
P.sub.W : instantaneous injection energy PA1 V: arc voltage PA1 I: current PA1 V.multidot.I: instantaneous electric energy injected into the arc PA1 P.sub.K : quantity of instantaneous energy which is carried by the metallic particles of mg scattering at a speed v PA1 m.multidot.C.sub.p .multidot.T: quantity of instantaneous energy carried away by the gas (the gas of the metallic particles) of constant-pressure specific head C.sub.p PA1 pth: quantity of instantaneous energy carried away from the arc space to the contactor via thermal conduction PA1 P.sub.R : quantity of instantaneous energy irradiated directly from the arc via light PA1 (1) Absorption at the wall surface PA1 (2) Absorption by the arc space and peripheral (high temperature) gas space and hence by the gas space PA1 Ia: absorption energy by gas PA1 Ae: absorption probability PA1 Iin: irradiated light energy PA1 n: particle density PA1 L: length of light path of the light
The above quantities vary according to the shape of the contactors and the length of the arc. When the length of the arc is 10 to 20 mm, P.sub.K =10 to 20%, pth=5%, and P.sub.R =75 to 85%.
The state in which the arc A is enclosed in the container 3 is shown in FIG. 5. When the arc A is enclosed in the container 3, the space in the container 3 is filled with the metallic particles and reaches a high temperature. The above state is strong particularly in the gas space Q (the space Q designated by hatched lines in FIG. 5) in the periphery of the arc positive column A. The light irradiated from the arc A is irradiated from the arc positive column A to the wall of the container 3, and is reflected at the wall. The reflected light is scattered, is passed again through the high temperature space in which the metallic particles are filled, and is again irradiated to the wall surface. Such reflections are repeated until the quantity of light becomes zero. The path of the light in this case is shown by Ra, Rb, Rc and Rd in FIG. 5.
The consumption of the light irradiated from the arc A is by the following ways.
The light irradiated from the arc includes wavelengths from far ultraviolet rays less than 2000 .ANG. to far infrared rays more than 1 .mu.m including all wavelengths in the range of continous spectra and linear spectra. The wall surface of the general container has a light absorption capability only in the range of approx. 4000 .ANG. to 5500 .ANG. even if the surface is black, and partly absorbs in the other range, but mostly reflects. However, the absorptions in the arc space and the peripheral high temperature gas space are as below.
When the light of wavelength .lambda. is irradiated to the gas space having a length L, and uniform composition and temperature, the quantity of light absorption by the gas space can be calculated as below. EQU Ia-A.multidot.n.multidot.LIin (1)
where
However, the formula (1) represents the quantity of absorption energy for a special wavelength .lambda.. The term Ae is the absorption probability of the special wavelength .lambda., and is a function of the wavelength .lambda., gas temperature and type of the particles.
In the formula (1), the absorption coefficient becomes the largest value for the gas the same as the light source gas for irradiating the light (i.e., the type and the temperature of the particles are the same) in both the continuous spectra and the linear spectra according to the teaching of the quantum mechanics. In other words, the arc space and the peripheral gas space absorb most of the light irradiated from the arc space.
In the formula (1), the quantity Ia of the absorption energy of the light is proportional to the length L of the light path. As shown in FIG. 5, when the light from the arc space is reflected at the wall surface, the L in the formula (1) is increased by the number of reflections of the light, and the quantity of the light energy absorbed at the high temperature section of the arc space is increased.
This means that the energy of the light irradiated by the arc A is eventually absorbed by the gas in the container 3, thereby raising the gas temperature and accordingly the gas pressure.
It the present invention, in order to effectively absorb the energy of the light which reaches approx. 70% of the energy injected into the arc, a special material is used in in which that one or more types fiber, net and highly porous material having more than 35% of porosity for effectively absorbing the light irradiated from the arc are selectively disposed at a special position for receiving the energy of the light of the arc in the container of the circuit breaker, thereby absorbing a great deal of the light in the container to lower the temperature of the gas space and to lower the pressure.
The above-described fiber is selected from an inorganic series of materials, metals, composite materials, woven materials and non-woven fabric, and is required to have thermal strength since it is installed in the space which is exposed to the high temperature arc.
Of the above-described materials of the fiber and the net, the inorganic series of materials adaptively include ceramic, carbon, asbestos, and the optimum metals include Fe, Cu, and may include plated Zn or Ni.
The highly porous blank generally has materials of the ranges of metals, inorganic series and organic series of the materials which have a number of fine holes in a solid structure, and are classified according to the relationship between the material and the fine holes into material which contains as a main body sold particles sintered and solidified at the contacting points therebetween and material which contains in a main body holes in such a manner that the partition walls forming the holes are solid material. In the present invention, the blank means the material before it is machined to a concrete shape, so-called "a material".
When the blanks are further more particularly classified, the blanks can be classified into the blank in which the gaps among the particles exists as fine holes, the blanks in which the gaps among the articles commonly exist as fine holes in the particles, and the blanks which contain foamed holes therein. The blanks are largely classified into the blank which has air permeability and water permeability, and the blanks which have individual pores independent of each other having no air permeability.
The shape of the above fine holes is very complicated and is largely classified into open holes and closed holes, the structures of which are expressed by the volume of the fine holes or porosity, the diameter of the fine holes and the distribution of the diameters of the fine holes and specific surface area.
The true porosity is expressed by the void volume which is the fine hole volume of all the open and closed holes contained in the porous blank with respect to the total volume (bulk volume) of the blank, i.e., percentage, which is measured by a substitution method and an absorption method with liquid or gas, but can be calculated as described below as defined in the method of measuring the specific weight and the porosity of refractory heat insulating brick of JIS R 2614 (Japanese Industrial Standard, the Ceramic Industry No. 2614). ##EQU1##
The apparent porosity is expressed by the void volume which is the volume of the open holes with respect to the total volume (bulk volume) of the blank, i.e., percentage, which can be calculated as described below as defined by the method of measuring the apparent porosity, absorption rate and specific weight of a refractory heat insulating brick of JIS R 2205 (Japanese Industrial Standard, the Ceramic Industry No. 2205). The apparent porosity may also be defined as the effective porosity. ##EQU2##
The diameter of the fine holes is obtained by the measured values of the volume of the fine holes and the specific surface area, and includes several .ANG. (Angstrom) to several mm from the size near the size of an atom or ion to the boundary gap of the particles group, and which is generally defined as the mean value of the distribution. The diameter of the fine holes of the porous blank can be obtained by measuring the shape, size and distribution of the pores with a microscope, or by a mercury press-fitting method. In order to accurately know the shape of the pores, it is generally preferable to employ a microscope as a direct method.
The measurement of the specific surface area is performed frequently by a BET method which obtains the area by utilizing adsorption isothermal lines in the respective temperatures of various adsorption gases, and nitrogen gas is frequently used.
The patterns of the absorption of the energy of the light and the decrease of the gas pressure by the adsorption using the special material of the present invention will be described in connection with an example of an inorganic porous material.
FIG. 6 is a perspective view showing an inorganic porous blank, and FIG. 7 is an enlarged fragmentary sectional view of FIG. 6. In FIGS. 6 and 7, numeral 13 designates an inorganic porous blank, and numeral 34 open holes communicating with the surface of the blank. The diameters of the hole 34 are distributed in the range from several microns to several mm in a random manner.
When the light is incident to the hole 34 when the light is incident to the blank 33 as designated by R in FIG. 7, the light is irradiated to the wall surface of the blank, is then reflected on the wall surface, is reflected in multiple ways in the hole and is eventually absorbed 100% by the wall surface. In other words, the light incident to the hole 34 is absorbed directly by the surface of the blank, and becomes heat in the hole.
FIG. 8 shows a characteristic curve diagram of the variation in the pressure in a model container in which the inorganic porous material is placed when the apparent porosity of the material is varied. In FIG. 8, the abscissa is the apparent porosity, and the ordinate expresses the pressure with the pressure when the porosity is 0 being that when the inner wall of the container is formed of metal such as Cu, Fe or Al and being set as 1 as a reference. As the experimental conditions, AgW contacts are installed at a predetermined gap of 10 mm in a sealed container in the shape of a cube 10 cm on each side, an arc of sinusoidal wave current of 10 kA peak value is produced for 8 msec, and the pressure in the container produced by the energy of the arc is measured.
The inorganic porous material used in the above embodiment is porous porcelain which is prepared by forming and sintering cordierte as the raw material of the porcelain of to which has been added inflammable material or foaming agent thereto to from the porous material, which has five holes with a mean diameter of 10 to 300 microns. Blanks having apparent porosites of 20, 30, 35, 40, 45, 50, 60, 70, 80 and 85% and the size of 50 mm.times.50 mm.times.4 mm (thickness) were prepared and disposed on the wall surface of the container to cover 50% of the surface area of the inner surface of the container.
The diameter of the fine holes should be a mean diameter which slightly exceeds the range of the wavelength of the light to be absorbed, and the rate of the fine holes occupying the surface, i.e., the degree of the specific surface area of the fine holes is important. In the absorption of the light in the fine holes, the deep holes are more effective and communicating pores are preferable. Since the light irradiated by the switch from the arc A is distributed in the range of several hundreds .ANG. to 10000 .ANG. (1 .mu.m), fine holes of several thousands .ANG. to several 1000 .mu.m of mean diameter, which slightly exceeds the above wavelengths, are adequate, and a highly porous material which exceeds 35% apparent porosity in the area of the holes occupying the surface is good for absorbing the light irradiated from the arc A. The effect can be particularly increased when the upper limit of the diameter of the fine holes is in the range less than 1000 m and the specific surface area of the fine holes is larger. According to the experiments, it has been confirmed that a preferred absorbing characteristic can be obtained to the light irradiated from the arc in a material having a mean diameter of five holes in the range of 5 .mu.m to 1 mm. It has also been observed that a blank of glass having holes in the range of 5 or 20 .mu.m mean diameter absorbs the light irradiated from the arc A well.
As seen from the characteristic curve in FIG. 8, the pores of the inorganic porous material absorbs the light energy, and acts to lower the pressure in the circuit breaker, which reduction increases as the apparent porosity of the porous blank is increased, and increases remarkably as the porosity becomes larger than 35%, and continues in the range up to 85%. When the porosity is further increased, it is necessary to further increasing the thickness of the porous material.
When the porosity is increased the relationship between the apparent porosity and the mechanical strength of the porous blank is such that the blank becomes brittle, the thermal conductivity of the blank decreases, and the blank becomes readily fusible by the high heat. When the porosity is decreased, the effect of reducing the pressure in the circuit breaker is reduced. Accordingly, the optimum apparent porosity of the porous blank for the practical use is in the range of 40 to 70% which is highly porous material.
The characteristic trend of FIG. 8 can also be applied to the general inorganic porous materials, and this can be assumed from the above description as to the absorption of the light.
Some prior-art circuit breakers use the inorganic material, but the object is mainly to protect the organic material container against the arc A, and the necessary characteristics include arc resistance, lifetime, thermal conduction, mechanical strength, insulation and carbonization resistance. The inorganic material which satisfies these requirements is composed of a material which has a relatively low porosity, and the purpose is different from the object of the present invention, and the apparent porosity of the prior-art material is approx. 20%.
The highly porous blanks are made of materials from the inorganic, metallic and organic series, of materials and the inorganic materials are particularly characterized as having insulation and high melting point properties. These two characteristics are useful for the material to be installed in the container of the circuit breaker. In other words, since the blank is electrically insulating, which does have an adverse influence an the breakage, and since the blank has a high melting point, the blank does not become molten nor produce gas, even if the blank is exposed to high temperature, and the blank is optimum as a pressure suppressing material.
The inorganic porous material can be porous porcelain, refractory material, glass, and cured cement, all of which can be used to decrease the gas pressure in the circuit breaker.